The present invention relates to an electro-mechanical and acoustic transducer for a portable terminal unit which can generate both vibration and sound by an alternating electric signal and a portable terminal unit in which the transducer is built. The portable terminal unit is, for instance, a portable telephone unit, a pager and a computer having a transmitter and a receiver, and the portable terminal unit performs communication with other distant unit on being carried with the user or placed in the vicinity of the user.
Conventionally, in a portable terminal unit such as a portable telephone unit, a small-size sound generator for generating bell sound and a micrometer for generating vibration to which a weight is attached tilting relative to axis of rotation are provided independently as means for informing the user of an incoming call.
In order to reduce the size and weight of the portable terminal unit, for the purpose of reducing the number of units, a prior art electro-mechanical and acoustic transducer of which generates both sound and vibration in a single unit has been devised and disclosed in Japanese Laid-open Utility Model Publication Number H5-85192.
In the prior art, when an alternating electric signal is input to a voice coil of the electro-mechanical and acoustic transducer, a force acts between the voice coil and a magnetic circuit unit. Since the electric signal which is input to the voice coil is electric signal of alternating current, the magnitude of the force varies with frequency of the alternating current. Consequently, a magnet held by a suspension is vibrated by the force acting on the magnetic circuit unit. This vibration is transmitted to a case through the suspension. As a result, the case vibrates.
The magnitude of vibration of mechanical vibration system is proportional to the sum of the masses of the magnet and the suspension of the mechanical vibration system. Since the mass of the suspension is small, the magnitude of vibration susbstantially depends on the mass of the magnet. However, since the mass of the magnet is not sufficient, the sufficient magnitude of vibration is not obtained form the mechanical vibration system even when the frequency of the electric signal which is input to the voice coil coincides with the resonance frequency of the mechanical vibration system. Therefore, when the electro-mechanical and acoustic transducer is provided in the portable telephone unit with a mass as much as 150 g, it is difficult to inform the user of the incoming call with sufficiently strong vibration.